The present invention relates generally to valve lifters for use in internal combustion engines. More particularly, the present invention relates to an axleless roller valve lifter.
Internal combustion engines typically comprise two or more valves associated with each cylinder to regulate intake and exhaust to and from the cylinder. The valves are commonly opened and closed by the rotation of a camshaft comprising a plurality of eccentric cams disposed on a shaft which rotates synchronously with the engine. A valve lifter is associated with each valve, with each lifter in contact at one end with one cam of the camshaft, the other end of the lifter is typically connected to or engages with a push rod, which in turn is connected to a spring-biased rocker arm assembly which actuates the corresponding valve. The spring bias typically maintains the valve in a normally closed position until the valve is opened upon actuation via the lifter. Thus, rotational motion of the camshaft translates into linear motion of the valve, which opens and closes as the camshaft rotates.
Valve lifters known in the art typically employ a roller wheel suspended on an axle attached to the lower end of the lifter body. The roller wheel contacts and rolls across the surface of the eccentric cam so that the lifter body raises and lowers in unison with the cam to actuate a push rod and rocker arm as described above. A series of needle bearings positioned radially around an axial center of the roller wheel enables the roller wheel to rotate freely about an axle, with the ends of the axle supported by arms or tabs extending from the lower portion of the lifter body. Thus, the needle bearings are in metal-to-metal contact with the axis of the roller wheel with oil introduced into the bearings providing some cooling by transferring heat from the bearings.
While conventional valve lifters generally perform their intended function, they are not without drawbacks. Because the needle bearings are in physical contact with the roller and the axle, there is continuous frictional wear between those contacting surfaces during operation of the engine. That wear is exacerbated during each lift and engine combustion cycle when additional forces are imparted to the needle bearings. Thus, the needle bearings and roller wear relatively quickly, particularly in high-performance applications. In those applications, such as drag racing, race teams often replace the lifters after a few runs rather than risk the inevitable failure of a worn lifter.
Thus, it can be seen that there remains a need in the art for an improved roller valve lifter.